Pathologists examine specimens—otherwise referred to herein as samples—to determine the type and extent of disease in order to identify the best approach for treatment. With improvements in pathological procedures, cellular features of diseases may be identified in specimens to make diagnoses based on only a few cells.
Typically, specimens are examined using a light microscope in order to diagnose or detect disease. The specimen is retrieved from a patient and processed for microscopic examination. A variety of minimally invasive techniques are available for retrieving cell sample specimens from a patient. For example, specimens may be retrieved by using fine needle aspiration or by brushing body cavity surfaces such as through endoscopic techniques. After the specimens are retrieved, the cells are prepared for evaluation. A number of preparation techniques are known—such as the Cytospin® technique and the ThinPrep® technique—for depositing cellular materials and/or tissue fragments onto a microscope slide. Another technique, commonly referred to as a cellblock preparation, isolates and immobilizes cellular materials and/or small tissue fragments. Cellular materials and/or small tissue fragments may be isolated using centrifugation and/or manually embedded within a solid support structure such as paraffin wax. Thin sections of the cellblock are then cut and placed or secured onto a microscope slide—a thin flat piece of glass—for examination under a microscope. Microscope slides are often used together with a cover slip or cover glass—a thinner flat piece of glass—that is placed over the specimen. Slides may be held in place on the stage of the microscope by slide clips or slide clamps.
Cervical cancer is just one type of disease that is detected or diagnosed through the examination of specimens. Although the invention is discussed herein with respect to cervical cancer, any disease is contemplated. In the 1930s, cervical cancer was the most common cause of cancer deaths in women in the United States. Today, cervical cancer is not even in the top ten. The significant decline in both the incidence and mortality of cervical cancer is attributed to the Papanicolaou test, or Pap test—also called Pap smear, cervical smear, or smear test—, which is a screening test used in gynecology to detect premalignant and malignant cells in the ectocervix and endocervix.
The Pap smear has been proven to be the most useful test for the detection of precancerous and cancerous lesions of the cervix. It is estimated that over 3.5 million women in the United States each year have an abnormal Pap smear. The Bethesda System (“TBS”) is a system for reporting Pap smear results. Abnormal results include Atypical Squamous Cells of Undetermined Significance (“ASC-US”) and Atypical Squamous Cells—Cannot Exclude High Grade Squamous Intraepithelial Lesion (“ASC-H”). Abnormal results further include Low Grade Squamous Intraepithelial Lesion (“LGSIL”), High Grade Squamous Intraepithelial Lesion (“HGSIL”), Squamous cell carcinoma, Atypical Glandular Cells Not Otherwise Specified (“AGC-NOS”), Atypical Glandular Cells, Suspicious for AIS or Cancer (“AGC-neoplastic”), and Adenocarcinoma in situ (“AIS”). LGSIL indicates mild dysplasia (“CIN 1”) including that caused by a Human Papillomavirus (“HPV”) infection. HGSIL indicates moderate dysplasia (“CIN 2”) or severe dysplasia (“CIN 3”) and may include carcinoma in situ as well as features suspicious for invasion, glandular cell including atypical such as endocervical cells, endometrial cells, glandular cells, endocervical cells favor neoplastic, glandular cells favor neoplastic, or adenocarcinoma in situ or adenocarcinoma (Endocervical, Endometrial, Extrauterine, Not otherwise specified).
Current techniques for obtaining Pap test samples include the conventional smear and the more recently preferred liquid-based procedures. The conventional smears are often obtained using a combination of a plastic spatula, brush or a broom-like brush in which the tissue surface is scraped. The cells obtained require immediate coating fixation with ethanol and polyethylene followed by submersion in 95% ethanol to prevent air-drying artifact that may interfere with appropriate evaluation of the samples.
Poor sensitivity of the conventional smears became apparent in the 1990's. Several studies have shown that the mean sensitivity of the conventional smear ranged from 37% at worst to 73% at best. When sources of errors with the conventional smear were analyzed, it was discovered that sampling and/or preparation errors were responsible for about two-thirds of false negative cases. In those situations, cells were either not collected properly or cells that were collected were not properly transferred to slides. Screening and/or interpretive errors were the cause for the remaining one-third of false negative cases. Abnormal cells were either missed by the cytotechnologist/pathologist or were incorrectly classified because of poor preservation. Due to the problems with conventional techniques liquid-based procedures were developed in which body fluids are collected.
The liquid-based procedures mitigated sampling errors and improved cell preservation. Cell preservation was improved through randomized representation and even distribution of cells with minimization of obscuring material such as inflammation, blood, and debris. With respect to Pap smears, liquid-based procedures are significantly more effective in detecting LGSIL and HGSIL and are as effective as conventional smears in detecting endocervical lesions.
Despite its proven value, the Pap test remains less than optimal. Sensitivity of the Pap test continues to be a subject of concern. False negative and false positive results of various values are reported and inter-observer reproducibility remains less than perfect. The greatest disagreement involves the results interpreted as ASCUS.
It has recently been proposed that HPV testing is of potential value in the screening of cervical cancer precursors. Several studies have shown that a combination of HPV testing and repeated cytologic screening provides reasonable sensitive screening for cervical neoplasia while limiting the use of colposcopic services, which are currently burdened. HPV testing appears to provide an objective assessment of neoplasia risk. A major advantage of this test is its potential for “reflex testing” when used in liquid-based cytology. Reflex testing for HPV is currently recommended by many clinicians and is considered routine in many centers all over the world. HPV-negative patients could be triaged to yearly follow-ups, while HPV-positive patients would require further colposcopic evaluation. Current commercially available HPV tests include the DiGene HPV Test with Hybrid Capture II (“HC2”), Cervista HPV, INFORM HPV in situ hybridization test as well as a variety of molecular HPV DNA assays.
Currently there are several automated screening devices that utilize digital images of specimens for evaluation. Digital pathology is rapidly gaining momentum as a proven and essential technology that assists with reducing laboratory expenses, improving operational efficiency, enhancing productivity, and improving treatment decisions and patient care. It is used worldwide in drug development, reference labs, hospitals, and academic medical center settings.
Digital pathology includes the use of automated screening devices that combine robotics, automated microscopes, high-performance cameras for image capturing and sophisticated computer algorithms for high-speed analysis. Automated screening devices have several advantages including easier location of abnormal and rare cytologic findings as well as coupling automated screening with cytotechnologist skills.
Currently there are two systems approved by the FDA in the United States for automated screening of Pap smears—the FocalPoint Slide Profiler and the ThinPrep® Imaging system.
In 1998, the Food and Drug Administration (“FDA”) approved the AutoPap system—the the forerunner of the FocalPoint Slide Profiler—as a system to rank and score Pap smear specimens according to their likelihood of being abnormal. Each specimen is classified into one of two groups: “Review” and “No Further Review”. The “Review” specimens are then ranked into five quintiles based on the severity of the abnormality.
The ThinPrep® Imaging system consists of two elements: an image processor and a review scope. Only specially prepared specimens using a synthetic nuclear dye “ThinPrep® Stain” may be used for analysis with this system. Up to 288 slides may be loaded on the system at a time. The image processor identifies 22 microscopic fields, which are reviewed by a cytotechnologist with an automated review scope. Results are then reported as either “normal” or “abnormal”, with “abnormal” cases undergoing full glass slide screening for diagnosis.
The impact of digital imaging on routine day-to-day cytology remains far from perfect. Problems with digital imaging for routine cytology is due, in part, to inexperience, poor reproducibility, poor image quality, under representation or under-diagnosis of lesions and the length of time required for capturing images (in addition to the realization that fewer than 5% of women in underdeveloped and developing countries have ever had a Pap test).
Therefore, there is a demand for an improved screening and diagnostic tool used in cytopathology, for example alternative methods to routine Pap tests. The improved screening and diagnostic tool of the present invention satisfies this demand by using digital imaging technology to overcome current limitations with cytologic specimens.